Self-developing film units of the integral type, i.e., the film unit is not peeled apart to view the final image, have become very popular since the introduction of Polaroid SX-70 film in 1972. These film units comprise two sheets, i.e., sheet-like elements, held in superposed relationship before, during and after exposure and processing (development). A rupturable container, or pod, releasably holding a processing composition is mounted at one end of the film unit (the leading end), positioned to distribute the processing composition between the superposed sheets. A trap to receive excess processing fluid is mounted at the opposite, or trailing, end of the film unit from the pod. All four edges are sealed to prevent leakage of the processing fluid and to help maintain the integrity of the developed picture. The assemblage may be held together by a mask having an aperture defining the image area. The layers carried on the inner surfaces of the two sheets include the appropriate silver halide emulsion layer(s), the appropriate image-receiving layer for forming a positive image by transfer (unless there is no image transfer, i.e., only a negative image is being formed) and the image-providing materials, usually preformed dyes or dye intermediates or precursors, and the other components as appropriate for the particular image-forming process. When the exposed film unit is advanced pod-end first between a pair of pressure-applying members, e.g., pressure rollers, the pod is ruptured and the released processing fluid is distributed or spread in a thin layer of predetermined thickness between the superposed sheets, any excess fluid being collected in the trap. The thickness of the applied layer of processing fluid is determined, at least in part, by the combined thicknesses of the mask and rail, if any, making up the thickness of the lateral border area. Special configurations may be given to the rollers to ensure that the processing fluid is spread in desired thickness.
Integral film units of the above type wherein exposure and image viewing are effected from the same side of the film unit are described, for example, in U.S. Pat. No. 3,415,644 issued Dec. 10, 1968 to Edwin H. Land, U.S. Pat. No. 3,652,268 issued Mar. 28, 1972 to Albert J. Bachelder and Frederick J. Binda, U.S. Pat. No. 3,761,268 issued Sept. 25, 1973 to Edwin H. Land and Richard J. Chen, and U.S. Pat. No. 4,356,248 issued Oct. 26, 1982 to Thomas P. McCole. Integral film units wherein exposure and viewing are effected from opposite sides are described, for example, in U.S. Pat. No. 3,594,165 issued Jul. 20, 1971 to Howard G. Rogers, and in U.S. Pat. No. 4,042,395 issued Aug. 16, 1977 to Frederick F. Tone, et al.
Film units of the type described in the above-noted Land U.S. Pat. No. 3,415,644 were initially commercialized as Polaroid SX-70 film and have included a mask member overlying the positive sheet and extending around the four edges of the film unit, as more clearly shown, for example, in the above-mentioned McCole U.S. Pat. No. 4,356,248. Spacer elements or rails positioned along the lateral edges of the film unit and designed to control the thickness of the applied layer of processing composition by controlling the spacing apart of the pressure rollers have been positioned under the folded-over mask edge, as in the above-noted McCole U.S. Pat. No. 4,356,248, or between the superposed sheets, as disclosed in the above-noted Bachelder, et al. U.S. Pat. No. 3,652,281 (note FIG. 4).
Film units of the type described in the above noted Tone, et al. U.S. Pat. 4,042,395 and originally commercialized as Kodak PR-10 film have utilized an image area-defining member or mask positioned between the lateral edges of the superposed sheets and which was wrapped around the leading and trailing ends to form pod and trap areas. In such a construction, the mask also may serve as a rail or a separate rail may be utilized in combination with the mask and also positioned between the lateral edges of the superposed sheets, as shown, for example, in U.S. Pat. No. 4,017,879 issued April 12, 1977 to Peter Lermann, et al. and in U.S. Pat. No. 4,460,255 issued July 17, 1984 to Katsuya Kozai, et al.
As shown, for example, in the above-noted Land, et al. U.S. Pat. No. 3,761,268, the photosensitive element may be shorter than the positive element.